Win32: Reduce section alignment for Windows.

Maximum alignment for Win32 is 16, so don't try
to set it to 32. Otherwise the compiler complains:

exec.c:102: warning: alignment of 'code_gen_prologue'
is greater than maximum object file alignment.  Using 16
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

exec.c

@@ -94,6 +94,10 @@ spinlock_t tb_lock = SPIN_LOCK_UNLOCKED;
 #define code_gen_section                                \
     __attribute__((__section__(".gen_code")))           \
     __attribute__((aligned (32)))
+#elif defined(_WIN32)
+/* Maximum alignment for Win32 is 16. */
+#define code_gen_section                                \
+    __attribute__((aligned (16)))
 #else
 #define code_gen_section                                \
     __attribute__((aligned (32)))